Question: Why do astronauts get pain in their backs?

Andrew Winnard answered on 7 Dec 2015:

Because there is no gravity pushing down on their bodies, they actually grow a few centimeters taller! This happens for a couple of reasons. Take a look at your friend or teacher and you might be able to see the back usually curves in a bit at the bottom, curves out around the chest then back in just below the head. This is called posture 🙂 Astronauts tend to loose their posture and there back becomes one long forward curve. There are also little discs between the back bones that normally get squashed small due to gravity pulling us downwards. In astronauts these also expand due to the lack of weight pushing down.

So their backs get longer, this stretches out the muscles too. Also they stop using the muscles that normally control posture and keep the back stable.

So as things stretch out they can get pain in their backs. When they come back to Earth they then need to learn to switch all the muscles back on, get them back to being strong and learn how to control their posture again. This is where I can help them with exercise! It is hoped that FRED might be able to to all this in one exercise in the future and we are doing science experiments to try and find that out!